1. Field of the Invention
The present invention relates to a method of processing a signal representing an input sound signal, the signal being divided in time into a plurality of signal segments, each having an individual duration of time, the signal segments being processed into an output signal of successive signal segments, the signal segments being processed in such a way that at least one, preferably all signal segments are repeated at least once in said output signal.
Moreover, the present invention relates an apparatus, and in particular to an electronic stethoscope for use in cardiology.
2. Description of Relation Art
Through the recent years physicians have been provided with an impressive arsenal of instrumentation for the diagnosis of cardiovascular diseases. Such an instrument is the well known stethoscope used to detect sounds originating from the heart and adjacent large vessels. Sound monitoring of the heart, or auscultation in general, is an important aspect in the evaluation of the physical condition of an individual, and is particularly important in the diagnosis of certain pathological conditions which manifest themselves by abnormal sounds.
When using a normal bifurcated stethoscope with binaural earpieces and a bell or diaphragm for receiving the sound signal, it is difficult to distinguish the sound elements in fast beating hearts, e.g. infants, but also when auscultating patients with a ‘normal’ heart rate, it can be difficult to observe split heart sounds or a weak murmur located near a primary heart sound.
Today it is possible to process the information residing in the auscultation signal electronically by using knowledge obtained by clinical research. Electronic stethoscopes make it possible to modify the physiological signal, but the approaches are mostly based on changes of the frequency components in the signal, which makes it difficult for a physician, trained in the use of the conventional stethoscopes, to recognize the signal.
This leads to the goal of creating a stethoscope or an apparatus for auscultation in general that makes it easier for the pathologist to distinguish between the different sound elements in even fast heart sounds. Since the pathologists partly base their diagnosis on the heart sounds, it is of great importance that an exact reproduction of the sound elements in the sound signal is performed, meaning that there should be no change in the pitch of the signal and no dissonance should be added as a result of the reproduction algorithm. If either distortion or change of pitch is present, it could lead to a wrong interpretation of the heart sounds, resulting in incorrect diagnoses by the physicians.
U.S. Pat. No. 4,528,689 discloses the idea of a method for artificially slowing down an analyzed sound signal. It is done by first low-pass filtering the sound signal from the heart and then splitting the signal, which varies cyclically from zero crossing to zero crossing, into a number of cycles, and each cycle is repeated successively. These repetitions of half-periods of a sound representing signal result in a slow version of the original sound having the original pitch.